Stepping up its preparations for a possible strike on Iran's nuclear facilities, the United States is transporting hundreds of 387 'bunker-buster' bombs to its air base on the British island of Diego Garcia in the Indian Ocean, a media report has claimed.

The US government signed a contract in January with Superior Maritime Services to transport 10 ammunition containers to Diego Garcia from Concord, California, Sunday Herald has reported.

The shipment includes 195 smart, guided Blu-110 bombs and 192 Blu-117 2,000 lb bombs.

The key Iranian nuclear facilities are said to be underground and both these type of bombs are effective against reinforced or underground facilities.

The United States and Israel have repeatedly asserted that they do not rule out a military action to stop Iran's nuclear ambitions and that they are keeping all the options on the table.

Contract details for the shipment were posted on an international tenders' website by the US Navy.

"They are gearing up totally for the destruction of Iran," Dan Plesch, director of the Centre for International Studies and Diplomacy at the University of London, said.

"US bombers are ready today to destroy 10,000 targets in Iran in a few hours," Plesch, who is the co-author of a recent study on the US preparations for an attack on Iran, stressed.

The final decision on whether to launch an attack would be in the hands of US President Barack Obama. He may decide that it would be better for the US to act instead of Israel, Plesch argued.

"The US is not publicising the scale of these preparations to deter Iran, tending to make confrontation more likely,"Plesch said adding, "The US is using its forces as part of an overall strategy of shaping Iran's actions."

Diego Garcia is a British territory about 1,000 miles south of India and Sri Lanka but is used as a US military base as part of an agreement reached in 1971.

It has already been used in operations against Iraq during the 1991 and 2003 Gulf wars.